The present invention relates generally to bearing assemblies, and, in particular, to devices and methods for configuring bearing assemblies with an improved wear ring liner.
Bearing assemblies allow a wheel to rotate about a shaft (also called an axle or journal). Bearing assemblies are often sealed to maintain a lubricant within the bearing assembly and to prevent dirt, sand, and moisture from entering the bearing assembly. The seal is typically formed of an annular rubber lip seal which rotates about the shaft. In some conventional arrangements, the annular rubber lip seal rotates about and contacts the shaft. See, for example, U.S. Pat. Nos. 2,208,482, 3,614,183, 3,717,394, 3,457,732, and 3,531,168. However, it was found that the annular rubber lip seal has a tendency to wear a groove into the shaft which may weaken the shaft and/or reduce the sealing efficiency of the seal. Since shafts are expensive to replace, this sealing arrangement was not optimal.
Other conventional arrangements fitted a metal sleeve (called a wear ring) tightly over the shaft to prevent damage to the shaft. The wear ring may be part of the bearing race or separate from the bearing race. See, for example, U.S. Pat. Nos. 5,380,102, 4,336,971, 4,235,485, 3,636,016, 3,021,161, 2,977,138, 2,875,004. In these embodiments, the annular rubber lip seal contacted the wear ring and thus prevented wearing away of the shaft by the seal. However the use of a wear ring created its own problem in that heavy loads and stresses on the wheel causes the shaft to flex and the annular rubber lip seal to pound against the wear ring. This action, in turn, caused the wear ring to impact on the shaft. This constant impact resulted in fretting (wearing away) of the shaft in the area where the wear ring is fitted over the shaft. As the fretting continues, eventually, the wear ring is no longer concentric with the shaft which eventually leads to seal failure.
Another conventional arrangement spaces the wear ring from the shaft at one end using a backing ring with a counter bore to center the wear ring about the shaft. The other end continues to be interference fit with the shaft. In this manner, the portion of the wear ring which is contacted by the annular rubber lip seal does not contact the shaft. There are a multitude of examples of this arrangement such as U.S. Pat. Nos. 2,879,114, 2,834,616, 3,612,547, 3,494,682, 3,741,615, and 5,024,449. Heat transfer bet ween the wear ring and the shaft is accomplished by contact with the backing ring, contact with the shaft, and vent holes which allow an oil or other lubricant to fill the void between the wear ring and the shaft. Although this wear ring arrangement has reduced fretting and continues to be used today, still some fretting remains where the wear ring contacts the shaft.
Other conventional arrangements configure the wear ring to include a wear ring liner, typically formed integral with an outer wear ring element, to prevent damage to the shaft. There are a multitude of examples of wear rings which include wear ring liners such as U.S. Pat. Nos. 5,211,406, 5,129,744, 4,936,591, 4,448,426, 4,552,367, 4,981,303, 4,696,479, 4,208,057, RE U.S. Pat. Nos. 33,029, 4,865,794, 4,721,312, 3,697,414, 3,580,093, 4,552,367, 4,856,794, 5,183,269, 5,201,528, 5,549,395, 5,350,181, 4,921,260, 3,011,814, 3,135,518, 4,428,586, 3,356,376, 5,582,412. Although wear rings which include wear ring liners prevent damage to the shaft, the liners are disadvantageous in that they also act as insulators or to block oil flow. Thus, the wear ring liners localize heat build-up at the critical location where the annular rubber lip seal rotates about the wear ring. This can lead to accelerated drying of lubricant from the annular rubber lip seal and eventually to premature failure of the seal. Accordingly, improved wear ring liners which prevent damage to the shaft and avoid localized heat are desirable.
U.S. Pat. No. 5,082,294, attempts to solve this problem by impregnating a polymeric wear ring liner with metallic particles. However, this solution is disadvantageous in that the heat transfer coefficient of the metal impregnated wear ring liners is not optimal. Further, the metal impregnated wear ring liners in accordance with this patent have increased cost, reduced resiliency, and increased abrasion properties. Accordingly, there exists a need for an improved low cost wear ring liner which has high heat transfer properties without the reduced resiliency, increased cost, and increased abrasion properties of the prior heat conductive wear ring liners.
Another conventional arrangement is where the wear ring is completely spaced from the shaft. See, for example, U.S. Pat. Nos. 4,692,040, and 5,017,025, as well as Japanese Patent Laid Open 46-17442. However, these arrangements are disadvantageous in that one or both ends of the wear ring is cantilevered without any support. The end which is left unsupported tends to wear the face of the bearing race to which it abuts. Thus, while spacing the wear ring from the shaft along its entire distance may prevent fretting about the shaft, it increases fretting of the face of the bearing race. Further, the wear ring may loose concentricity due to constant impacts which leads to premature seal failure. Additionally, this arrangement is disadvantageous because it is not always possible to precisely align the wear rings in the manner disclosed. This misalignment results in seal wear over time and eventual seal failure. Accordingly, there exists a need for an improved low cost wear ring which does not have a tendency to loose concentricity or wear the face of the bearing race.
Aspects of the present invention overcome one or more of the above mentioned problems by using improved bearing assemblies and/or improved wear ring liners. For example, an aspect of the present invention includes configuring a bearing assembly to include a wear ring having an integral wear ring liner which allows oil or other lubricants to pass along or through the wear ring. In aspects of the invention, the wear ring liner is of a low abrasion, low friction material such as a polymeric (e.g., nylon), synthetic rubber, elastomeric, graphite, and/or other low friction lining material. The low abrasion/friction liner material provides a cushioning between the wear ring and the shaft. Thus, fretting of the shaft is substantially reduced or eliminated while at the same time allowing the wear ring to derive its concentricity directly from the shaft.
In aspects of the invention, the wear ring liner is interference fit with the journal to maintain the wear ring liner concentric with the journal.
Methods and apparatus in accordance with the present invention increase longevity and integrity of wear ring seals and shaft. Further, maintenance time and associated repair costs are reduced.
In further aspects of the present invention, the wear rings include wear ring liners which are porous. The porous wear ring liners allow oil to flow through and contact the wear ring directly beneath the location of the wear ring which contacts the annular rubber lip seal. The lubricant acts as a heat conducting medium to transfer heat from the wear ring to the shaft, thus preventing premature failure of the wear ring seal. Thus, the present invention is a substantial improvement over any conventional wear ring liners.
In yet further aspects of the invention, deformations in the wear ring liner reduce friction as the wear ring is pressed onto the shaft. Since the deformations result in less surface area in contact with the shaft, friction is reduced.
In still further aspects of the invention, a chemical or ultrasonic bonding technique is utilized to make the wear ring liner integral with the wear ring. The use of an integral bonding technique allows the wear ring liner to be integrally bounded to the wear ring without any appreciable decrease in the overall thickness of the wear ring. Thus, the structural integrity of the wear ring is maintained.
In yet further aspects of the invention, the bearing assembly is configured such that the wear ring liner is restrained by the backing ring and/or the inner race to prevent the wear ring liner from becoming deformed.
These and other features of the invention will be apparent upon consideration of the following detailed description of preferred embodiments. Although the invention has been defined using the appended claims, these claims are exemplary in that the invention is intended to include the elements and steps described herein in any combination or subcombination. Accordingly, there are any number of alternative combinations for defining the invention, which incorporate one or more elements from the specification, including the description, claims, and drawings, in various combinations or subcombinations. It will be apparent to those skilled in roller bearing assembly theory and design, in light of the present specification, that alternate combinations of aspects of the invention, either alone or in combination with one or more elements or steps defined herein, may be utilized as modifications or alterations of the invention or as part of the invention, It is intended that the written description of the invention contained herein covers all such modifications and alterations.